API detect unexpected client disconnection

Legato Application Framework
1

Hiya,

What is the correct way to catch the unexpected/unclean removal of an API client form a server app?

Use case:

I have a server app that publishes an API.

When a client connects to the API (say using api_Open()), certain resources are locked by the server for the exclusive use of that client.

When the client closes cleanly, it should call api_Close() to indicate to the server that the resources are no longer required by the client and can be released for use by another client.

I need to trap the case where the client faults or otherwise exits without calling api_Close() so that the server can release the locked resources.

How can this be done?

Thanks, Dave

2

Hi David,

You need to create an event handler in the server side that will be called when a client application is terminated. Then, inside the event handler, you may clean the allocated resources properly.

To do so, first add a handler in the COMPONENT_INIT of your server:
le_msg_AddServiceCloseHandler(api_GetServiceRef(), CloseSessionEventHandler, NULL);

Then, inside the close session event handler, clean the allocated resources. You may need to add an extra field along with the resources to save the client reference when api_Open() is called. The event handler looks like this:

static void CloseSessionEventHandler
(
    le_msg_SessionRef_t sessionRef, ///< [IN] Message session reference.
    void* contextPtr                ///< [IN] Context pointer.
)
{
    if (!sessionRef)
    {
        LE_ERROR("ERROR sessionRef is NULL");
        return;
    }

    LE_DEBUG("SessionRef (%p) has been closed", sessionRef);
    //Clean resources allocated by this client
}

Hope this helps,
Regards,

3

Hi @oabid

Thanks. Much appreciated.

I’ll give it a go.

I assume that I can store the data reference I create when a component open()'s my service in the context of le_msg_AddServiceCloseHandler()?

ciao, Dave

4

Yes, it is possible to have the app client reference when it calls a server API. The function is called: api_GetClientSessioRef();